The present invention relates to aqueous suspensions comprising at least one alkaline compound (B) in combination with silica and/or alumina, to a process of use in the preparation of these compositions and to their uses in the field of cement pastes, mortars and concretes and in particular as setting and hardening accelerating agent for cements.
Conventionally, in the concrete industries, concrete or mortar layers are applied on a substrate or surface to be concreted with the help of two spraying techniques, one by the dry route and the other by the wet route.
Processes for concrete spraying by the dry route employ a dry mixture comprising all the conventional anhydrous components of a concrete or of a mortar. This is transported to a spray nozzle, where wetting with the mixing water is then carried out. A setting accelerating agent is generally added upstream or at the spray nozzle and the mixture obtained is sprayed onto the surface to be concreted. Unfortunately, with this type of process, a phenomenon of rebound of the concrete occurs which is harmful economically and which, furthermore, represents a risk to the safety of the operator carrying out the spraying.
The process for spraying by the wet route, which employs a cement mixture which is usually thoroughly wetted, allows the two problems mentioned above to be partly solved. However, the presence of an excess amount of water affects the relative density of the concrete or mortar and, on the other hand, the introduction of a setting accelerating agent in order to compensate for this effect is harmful to the mechanical strength over time of the concrete or mortar, once it has been sprayed.
Provision has recently been made, in Patent Applications EP 736,489 and EP 736,501, for the use of mixtures based on silica and on aluminium sulphate, which are provided in the form of a reversible gel, as substitution products for conventional setting accelerating agents in the concrete industries. This type of additive advantageously proves to be less corrosive than conventional setting accelerating agents and is furthermore satisfactory economically. On being present in the sprayed concrete, it significantly reduces the phenomenon of rebound mentioned above.
The Applicant has unexpectedly found a novel family of aqueous compositions based on specific aluminium derivatives which have an even better performance than those disclosed in Patent Application EP 736,501.
The first subject-matter of the present invention is thus an aqueous suspension comprising:
A) silica and/or alumina particles, and
B) a compound of general formula (I):
Al(OH)a(SO4)b(SiOx)c(Y)dxe2x80x83xe2x80x83(I)
xe2x80x83with:
a between 0.1 and 2,
b between 0.3 and 1.5,
c between 0 and 0.1,
d greater than 0.05,
Y chosen from alkali metals and alkaline earth metals,
x between 2 and 4, and its derivatives,
the said compound (B) being present in the suspension at a concentration of at least 1.65 mol/l, expressed as moles of aluminium issued from the said compound.
Y preferably represents a sodium atom.
The Applicant has unexpectedly found that the use of an aqueous suspension as defined above significantly increases the kinetics of curing of cement pastes, concrete or mortar, in comparison with conventional setting accelerating agents.
The examples presented below illustrate more specifically this setting accelerating effect of the suspensions according to the invention.
The compound (B) of general formula (I) comprises soluble species and solid species.
The soluble species are generally ions, indeed polyions, such as hydrolysis complexes, aluminium poly-sulphates, which optionally comprise silicates. The soluble species can be present individually within the solution or adsorbed on the silica or alumina particles.
The solid species are particles, of micron or nanometric size, of Al(OH)3, AlOOH and/or Al3(OH)6(S4)2Na, for example. In general, at least a portion of these solid species are amorphous, the others being crystal- line. These solid species can be dispersed within the dispersion or can interact with the silica or alumina particles.
According to a preferred embodiment of the invention, the compound (B) exhibits an amorphous structure after having been dried, the said structure representing at least 15% by weight of the compound (B).
More preferably, the compound (B) present in the claimed aqueous suspensions is at least partially in the form of an amorphous dispersed solid.
The amorphous nature of the dispersed solid is, within the meaning of the invention, that determined by X-rays. More specifically, the monitoring method is X-ray diffraction. On the X-ray spectrum, the amorphous nature is reflected by the presence of halos instead of the main lines. Monitoring can be carried out either on the dried suspension or on the suspension as is.
In the first case, the suspension is dried at room temperature so as to remove the free water but to retain the water of constitution of the components of the suspension. The X-ray spectrum obtained on the dry solid opens the way to the amount of crystalline solid and thus, by difference, to the amount of amorphous solid. It is necessary to remove, from this amount of amorphous solid, the amount of silica (it is amorphous) in the suspension, in order to obtain the amount of amorphous compound (B).
In the second case, the X-ray analysis is carried out directly on the aqueous suspension.
More preferably, the indices a and b present in the overall formula of the compound (B) are between approximately 0.75 and 2 and 0.3 and 1.2 respectively.
According to a preferred embodiment of the invention, the said suspension comprises approximately from 2.1 to 3.5 mol/l of aluminium, approximately from 2.25 to 4 mol/l of sulphate and approximately from 0.2 to 3.5 mol/l of silica.
The suspension according to the invention has a pH (measured according to ISO Standard 787/9) of between 2.5 and 4. According to a preferred embodiment of the invention, it has a value of between 3 and 4 and more preferably is of the order of 3.7.
The claimed aqueous suspensions advantageously constitute an optimum with respect to the compromise of the properties desired in the field of cements, mortars and concretes. These properties are accelerated hardening and setting kinetics and an increased mechanical strength of the cured grouts, mortars or concretes incorporating them.
An optimization in one of these kinetics is generally acquired at the expense of the mechanical strength, and vice versa. Surprisingly, the claimed aqueous suspensions significantly accelerate the hardening kinetics, in comparison with a conventional suspension based on a silica/aluminium sulphate mixture, without affecting the long-term mechanical properties of the mortars incorporating them. These properties remain entirely satisfactory. These results are presented in more detail in the examples below.
According to a privileged embodiment of the invention, the aqueous suspension comprises a compound (B) of general formula I in which a has a value of the order of 1.26xc2x10.1, 0.5xc2x10.1 or 0.88xc2x10.1.
The aqueous suspensions comprising a compound (B) of general formula I in which a is between 0.1 and 1.5, with the said suspension comprising approximately from 2.2 to 3.1 mol/l of aluminium and approximately 2.3 to 3.9 mol/l of sulphate, are more particularly preferred.
Mention will very particularly be made, as representative of the claimed aqueous suspensions, of the suspensions described in the examples below.
According to a preferred alternative form of the invention, the claimed aqueous suspensions exhibit a silica concentration of between approximately 0.7 and 2.4 mol/l.
The compound (B) is used in combination, in the aqueous suspensions provided according to the invention, with at least one compound selected from:
a silica, chosen in particular from fumed silicas, precipitated silicas, silica sols, silica gels, pyrogenic silicas, silica compounds of natural or synthetic origin, aluminosilicates, smectites, magnesium silicates, clays, wollastonite, talc, mica, attapulgite, sepiolite, montmorillonite or bentonites,
an alumina.
In addition, the aqueous suspensions according to the invention can comprise a metal or alkali metal sulphate of sodium sulphate, iron sulphate or aluminium sulphate type, and the like. It is preferably sodium sulphate.
The claimed suspensions can also incorporate calcium silicates and aluminates.
Thus, in the specific case where the aqueous suspension combines a observed with the compound (B), a beneficial effect is recorded on the activity as setting accelerating agent of the said suspension, which is reflected in particular by a significant decrease in the rebound phenomenon observed when concrete is sprayed.
As regards more particularly the silica included in the suspension according to the invention, a silica chosen from fumed silicas, precipitated silicas, silica compounds of natural or synthetic origin, comprising in particular silicas chosen from aluminosilicates, for example Tixosil 28(copyright) sold by Rhxc3x4ne-Poulenc, smectites, magnesium silicates in general, and their mixtures, is very particularly suitable. Use is preferably made, as silica, of at least one precipitated silica.
Precipitated silica is understood to mean, in this instance, a silica obtained by precipitation from the reaction of an alkali metal silicate with an acid, generally an inorganic acid, at an appropriate pH of the precipitation medium, in particular a basic, neutral or only slightly acidic pH.
The silica can be prepared in any way (addition of acid to a silicate vessel heel, simultaneous complete or partial addition of acid or silicate to a vessel heel of water or of silicate solution, and the like) and the preparation method is chosen as a function of the type of silica which it is desired to obtain. At the end of the precipitation stage, there is generally a stage of separation of the silica from the reaction mixture according to any known means, filter press or vacuum filter, for example; a filtration cake is thus collected, which cake is washed, if necessary; this cake, optionally after breaking up, can be dried by any known means, in particular by atomization, and then optionally milled and/or agglomerated. These combined procedures form the subject of a detailed description in Application EP 736,501, to which reference will be made.
The precipitated silica preferably present in the suspension according to the invention generally exhibits a CTAB specific surface of between 50 and 250 m2/g, in particular between 100 and 240 m2/g.
The suspension according to the invention advantageously comprises a precipitated silica having a very good ability to disperse and to deagglomerate.
A precipitated silica as disclosed in European Patent Application EP 520,862 can thus be employed.
The precipitated silicas disclosed in Application EP 736,489 can also be provided as representative of the precipitated silicas which can be employed in the claimed suspensions.
The silica, in particular the precipitated silica, present in the suspension according to the invention can be finely divided, in particular as the result of milling (for example wet milling) or deagglomeration with ultrasound.
A second aspect of the present invention relates to a process useful for the preparation of aqueous suspensions based on at least one compound (B) of general formula I as described above.
More specifically, another subject-matter of the present invention is a process useful for the preparation of an aqueous suspension as described above, characterized in that it comprises the stages consisting in:
Axe2x80x94mixing aluminium sulphate, silica and/or alumina particles, and optionally water;
Bxe2x80x94optionally adding, to the mixture obtained according to Stage A, an alkaline silicate in the form of an aqueous solution and homogenizing the said mixture at room temperature;
Cxe2x80x94adding, to the mixture obtained according to Stage B, an alkaline aluminate in the form of an aqueous solution, with vigorous stirring and at room temperature;
Dxe2x80x94bringing the combined mixture to a temperature of between 40 and 90xc2x0 C. and recovering the expected suspension.
According to a preferred alternative form of the invention, an aluminium sulphate is incorporated during the preparation process. This can be added either on a single occasion during one of the stages of the said process or on several occasions in Stages A, B, C and D of the process. It can be added in the powder or solution form.
Thus, it can be mixed either in the solid state, that is to say in the form of a powder, or in the molten state, that is to say in the form of a solution brought to a temperature of between 95+ C. and 130xc2x0 C.
More preferably, the aluminium sulphate is added in the form of a powder or of a solution during Stage A.
As regards the silica and/or the alumina employed in Stage A, they are introduced in the form of suspension(s) or of powder(s).
It is preferably an aqueous silica suspension and more preferably an aqueous suspension of a precipitated silica, such as those disclosed in Application EP 736,501. This aqueous precipitated silica suspension may have been obtained beforehand by mechanically breaking up a filtration cake resulting from a silica precipitation reaction. As regards the procedures for the preparation of such a filtration cake and for breaking up, reference will be made to the description in Application EP 736,489. The examples which appear below exhibit a specific embodiment of this process.
As regards stage B, use may be made, as silicate, of any common form of silicate, such as metasilicates, disilicate and advantageously an alkali metal M silicate, in which M is sodium or potassium.
The silicate preferably has a molar ratio Rm=SiO2/Na2O of between 3 and 3.8.
Stage B is preferably carried out at a temperature of between 10 and 40xc2x0 C. and more preferably at room temperature. The silicate is incorporated in the mixture of Stage A in the form of a concentrated solution and with vigorous mechanical stirring.
The third stage C relates to the incorporation of the aluminate. This is also added in the form of a concentrated solution and with vigorous stirring. As regards the method of stirring, it can be shearing applied by a homogenizer of UltraTurrax(copyright) type.
The so-obtained mixture is subjected, in Stage D, to a temperature treatment, so as to complete the homogenization of the combined reaction mixture. This heat treatment can, for example, consist of a temperature rise over one hour to a temperature of between 50 and 90xc2x0 C., preferably of the order of 65xc2x0 C., and the maintenance of the mixture at this temperature for approximately one hour, on completion of which the mixture is allowed to cool naturally.
It is clear that the silica, aluminium sulphate, silicate and aluminate concentrations are adjusted so as to obtain an aqueous suspension as characterized according to the present invention.
As stated previously, the claimed aqueous suspensions are particularly advantageous in the preparation of cement pastes, concretes and mortars.
The advantages obtained are due in part to the use of the compound (B) and are particularly optimized when the compound (B) is used in combination with silica and is provided in the form of a suspension as described above.
Consequently, another aspect of the present invention relates to the use of the compound (B) in the field of building materials.
Thus, it can be employed in the preparation of cement pastes (grouts or wetted compositions formed from cement and water and, optionally, conventional additives), mortars and concretes and more particularly as setting and/or hardening accelerating agent for cement pastes, mortars or concretes.
In these applications, the compound (B), preferably in the form of a suspension according to the invention, introduces noteworthy and unexpected advantages which are of particular interest in the field of sprayed grouts, mortars and concretes.
As explained above, the compound (B), preferably in the form of a suspension as claimed, constitutes an optimum with respect to the compromise in properties: kinetics of hardening/kinetics of setting/mechanical strength of the cured grouts, mortars or concretes.
Thus, in the specific case where the amount of compound (B) used to prepare the cement paste, mortar or concrete, expressed in moles, is greater than approximately 0.003 mol per 100 g of cement, a particularly rapid curing of the sprayed layer is observed, making it possible to work with maximum safety, for example under vaulting, from a few hours after spraying (application for the preparation of structural mortars, in particular).
The use of the aqueous suspensions described above is preferred. They do not damage the mechanical properties of the cement compositions in the long term. On the contrary, it is found that they result in high compressive strength values at 28 days, in particular when they are used in an amount such that the amount by mass of silica employed (expressed as anhydrous silica) is between 0.2 and 5%, in particular between 0.4 and 2.5%, with respect to the mass of cement employed to prepare the cement paste, mortar or concrete.
On this account, they are thus particularly advantageous in the application of layers of cement pastes, concretes or mortars by spraying techniques.
Firstly, they can be pumped perfectly well by conventionally used spraying equipment.
The health and safety conditions, in particular for the operator carrying out the spraying process, are improved due to the very weakly irritating nature of the suspension according to the invention by virtue in particular of its pH of between 2.5 and 4.
The use of the suspensions according to the invention makes it possible in addition to limit spraying losses by rebound and to obtain very thick sprayed layers, resulting in an increase in productivity. This is possible in particular by virtue of the homogeneity, the cohesion and/or the adhesion (sticky aspect) of these cement compositions.
They also promote cold weather concreting.
Finally, the suspensions according to the invention can be employed in the preparation of cement pastes (grouts or wetted compositions formed from cement and water and optionally conventional additives), mortars and concretes for the consolidation of oil wells.
In fact, following a drilling operation, cement has to be placed between the pipes, which have to case the well, and the wall of the hole in order to render this annular space leaktight. Depending on the depth of cement to be emplaced, specific additives can be added to the cement in order to adjust its hydraulic and mechanical characteristics, which are affected by the temperature and the pressure, which vary with the depth. In some cases, in particular in regions close to the seabed, where temperatures are in the region of 4xc2x0 C., the setting times of the mixtures are excessively long. It is then necessary to improve their homogeneity in the expectation of curing.
Use is preferably made of the suspensions according to the invention at a concentration, expressed in moles of compound (B) of general formula I of greater than approximately 0.003 mol per 100 g of Cement employed to prepare the cement paste, mortar or concrete. A particularly rapid curing of the mixture is thus obtained.
Another subject-matter of the present invention is a process for spraying concrete or mortar involving the application of a layer of concrete or mortar on a surface, characterized in that a compound (B) as described above is added just upstream or at the place of the spraying means. This process can be carried out by the dry route or, preferably, by the wet route.
According to a specific form of the invention, use is made of an amount such that the concentration in moles of the said compound (B) is greater than approxi- mately 0.003 mol per 100 g of cement employed to prepare the concrete or mortar.
The compound (B) is preferably introduced in the form of an aqueous suspension as defined above.
According to one embodiment of the invention, the process is carried out by the dry route.
Generally, a dry mixture of concrete or of mortar is then formed, the said mixture is transferred in order to be introduced into a spraying means, the compound (B), preferably in the form of an aqueous suspension in accordance with the invention, is added to the mixture just upstream or at the place of the spraying means and the resulting mixture is sprayed from the spraying means onto the surface or substrate to be coated.
The compound (B), preferably in the form of a claimed aqueous suspension in accordance with the invention, and the mixing water can be introduced into the dry mixture separately, that is to say by two different means (for example using two different pumps). They can also be introduced into the mixture jointly, that is to say by the same means; they are then in particular mixed with one another prior to their introduction into the said mixture. The use of the suspension according to the invention makes it possible to reduce the rebound and to decrease the formation of dust.
It should be noted that the claimed aqueous suspension can be employed, in particular, as mixing water.
Although the spraying process can be carried out by the dry route as described above, its implementation by the wet route gives particularly excellent results.
Thus, according to a preferred embodiment of the invention, the process is carried out by the wet route.
Generally, a mixture of wetted concrete or mortar is then formed, the said mixture is transferred in order to introduce it into a spraying means, the compound (B), preferably in the form of an aqueous suspension as claimed, is added to the said wetted mixture just before or at the spraying means and the resulting mixture is sprayed from the spraying means onto the surface (or substrate).
In both embodiments of the invention, the means used to form the dry mixture or the wetted mixture, to transfer and then introduce this mixture into the spraying means and to spray the mixture onto the surface to be concreted from the said means correspond to those commonly employed in the field of spraying concrete or mortar and are thus well known to the person skilled in the art.
Thus, the dry mixture and the wetted mixture are generally each formed by mixing the products of which they are composed; the said products can be introduced into the mixer in any order; for example, in the case of the wet-route spraying process, the aggregates (sand in the case of a mortar; coarser aggregates, such an gravel and/or pebbles, and generally sand, in the case of a concrete) and the cement are first mixed with one another, the water subsequently being introduced, and the wet mixture thus formed finally being mixed.
Additives, such as a plasticizer, for example, can optionally be incorporated at any appropriate time during the preparation of the dry mixture (dry-route process) or of the wetted mixture (wet-route process) Mention may be made, as plasticizers, of in particular melamine, sodium polynaphthalenesulphonate, sodium polyacrylate or sodium polycarboxylate.
It is also possible to incorporate reinforcing fibres, such as poly(vinyl alcohol) fibres, polypropylene fibres, steel fibres, polyacrylonitrile fibres, cellulose fibres, carbon fibres, Kevlar(copyright) fibres, polyamide fibres, polyethylene fibres, and the like.
Furthermore, in the case of the dry-route spraying process, the mixture formed under dry conditions is introduced into the spraying means generally after having been transported using a stream of compressed air in a pipe (or conduit); in the case of the wet-route process, the wetted mixture is introduced into the spraying means generally after having been conveyed using an appropriate pump, for example a piston pump or a screw pump, in a pipe (or conduit).
The compound (B), preferably in the form of an aqueous suspension in accordance with the invention, can be introduced just before or at the spraying means, for example via a metering pump.
The spraying means is usually composed of a spray nozzle; the combination formed from the dry mixture, the mixing water and the compound (B), preferably in the form of a claimed aqueous suspension, is then sprayed, from this spray nozzle, generally using propellent air which feeds the said nozzle, the propellent air usually being compressed air.
The use of the compound (B), preferably in the form of an aqueous suspension as defined according to the invention, and its point of introduction into the mixture are essential characteristics of the invention.
The examples and figures presented below illustrate the invention without, however, limiting the scope thereof.